linux-kernel - Re: [PATCH v7 2/2] s390/pci: Migrate s390 IRQ logic to IRQ domain API

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Message-Id: <DEOF3L4CJBHA.Q5OSQSIWCD0K@linux.ibm.com>
Date: Wed, 03 Dec 2025 08:53:24 +0100
From: "Tobias Schumacher" <ts@...ux.ibm.com>
To: "Gerd Bayer" <gbayer@...ux.ibm.com>,
        "Tobias Schumacher"
 <ts@...ux.ibm.com>,
        "Heiko Carstens" <hca@...ux.ibm.com>,
        "Vasily Gorbik"
 <gor@...ux.ibm.com>,
        "Alexander Gordeev" <agordeev@...ux.ibm.com>,
        "Christian Borntraeger" <borntraeger@...ux.ibm.com>,
        "Sven Schnelle"
 <svens@...ux.ibm.com>,
        "Niklas Schnelle" <schnelle@...ux.ibm.com>,
        "Gerald
 Schaefer" <gerald.schaefer@...ux.ibm.com>,
        "Halil Pasic"
 <pasic@...ux.ibm.com>,
        "Matthew Rosato" <mjrosato@...ux.ibm.com>,
        "Thomas
 Gleixner" <tglx@...utronix.de>
Cc: <linux-kernel@...r.kernel.org>, <linux-s390@...r.kernel.org>
Subject: Re: [PATCH v7 2/2] s390/pci: Migrate s390 IRQ logic to IRQ domain
 API

On Tue Dec 2, 2025 at 7:14 PM CET, Gerd Bayer wrote:
> On Thu, 2025-11-27 at 16:07 +0100, Tobias Schumacher wrote:
>   [ ... snip ... ]
>
>> diff --git a/arch/s390/pci/pci_irq.c b/arch/s390/pci/pci_irq.c
>> index e73be96ce5fe6473fc193d65b8f0ff635d6a98ba..2ac0fab605a83a2f06be6a0a68718e528125ced6 100644
>> --- a/arch/s390/pci/pci_irq.c
>> +++ b/arch/s390/pci/pci_irq.c
>> @@ -290,146 +325,196 @@ static int __alloc_airq(struct zpci_dev *zdev, int msi_vecs,
>>  	return 0;
>>  }
>>  
>> -int arch_setup_msi_irqs(struct pci_dev *pdev, int nvec, int type)
>> +bool arch_restore_msi_irqs(struct pci_dev *pdev)
>>  {
>> -	unsigned int hwirq, msi_vecs, irqs_per_msi, i, cpu;
>>  	struct zpci_dev *zdev = to_zpci(pdev);
>> -	struct msi_desc *msi;
>> -	struct msi_msg msg;
>> -	unsigned long bit;
>> -	int cpu_addr;
>> -	int rc, irq;
>>  
>> +	zpci_set_irq(zdev);
>> +	return true;
>> +}
>> 
>
> It's always a little tricky to distinguish which code handles both MSI
> and MSI-X or just MSI proper when routines have _msi_ in their name.
> But apparently, both __pci_restore_msi_state() and
> __pci_restore_msix_state() inside pci_restore_msi_state() do call
> arch_restore_msi_irqs() - so life is good!

Regarding arch_restore_msi_irqs() the main change in the patchset is
that it is now also conditionally  called from zpci_reenable_device().
This is becasue in the recovery case, __pci_restore_msix_state() does
not call arch_restore_msi_irqs(), it exits directly at the beginning
because dev->msix_enabled evaluates to false.

With the legacy API, IRQs are later re-enabled using
arch_setup_msi_irqs(), which also registers the airq with the hw. With
the MSI parent domain, zpci_msi_prepare() would register the airq, but
is not called in the recovery path. This is why it is now added to
zpci_reenable_device()


>   [ ... snip ... ]
>
>> +static void zpci_msi_domain_free(struct irq_domain *domain, unsigned int virq,
>> +				 unsigned int nr_irqs)
>> +{
>> +	struct irq_data *d;
>> +	int i;
>>  
>> -	return (zdev->msi_nr_irqs == nvec) ? 0 : zdev->msi_nr_irqs;
>> +	for (i = 0; i < nr_irqs; i++) {
>> +		d = irq_domain_get_irq_data(domain, virq + i);
>> +		irq_domain_reset_irq_data(d);
>
> Question: zpci_msi_alloc_domain() did modify airq data, can this be
> left as is in zpci_msi_domain_free()?

I was thinking about this myself and came to the conclusion that it is
fine. zpci_msi_domain_alloc() sets the ptr to the msi parent domain and
data to the encoded hwirq. Both fields are only required in the IRQ
handler.
* When free() is called, the corresponding interrupt was already
  deactivated by the hardware, so hardware shouldn't generate it
  anymore anyway.
* If, for whatever reason, hw still generates the interrupt,
  generic_handle_domain_irq returns an error since the hwirq cannot be
  resolved.
* If the IRQ gets allocated again, the fields are written again before
  the IRQ is activated. The data written will even be the same
  as it was before.

>    [ ... snip ... ]
>
>
>> +
>> +int zpci_create_parent_msi_domain(struct zpci_bus *zbus)
>> +{
>> +	char fwnode_name[18];
>>  
>> -	if (zdev->aisb != -1UL) {
>> -		zpci_ibv[zdev->aisb] = NULL;
>> -		airq_iv_free_bit(zpci_sbv, zdev->aisb);
>> -		zdev->aisb = -1UL;
>> +	snprintf(fwnode_name, sizeof(fwnode_name), "ZPCI_MSI_DOM_%04x", zbus->domain_nr);
>> +	struct irq_domain_info info = {
>> +		.fwnode		= irq_domain_alloc_named_fwnode(fwnode_name),
>> +		.ops		= &zpci_msi_domain_ops,
>> +	};
>> +
>> +	if (!info.fwnode) {
>> +		pr_err("Failed to allocate fwnode for MSI IRQ domain\n");
>> +		return -ENOMEM;
>>  	}
>> -	if (zdev->aibv) {
>> -		airq_iv_release(zdev->aibv);
>> -		zdev->aibv = NULL;
>> +
>> +	if (irq_delivery == FLOATING)
>> +		zpci_msi_parent_ops.required_flags |= MSI_FLAG_NO_AFFINITY;
>
> Add empty line here, so the intent is clear that the following
> assignment is executed unconditionally.

Ok.

>    [ ... snip ... ]
>  
>> @@ -466,6 +551,7 @@ static int __init zpci_directed_irq_init(void)
>>  		 * is only done on the first vector.
>>  		 */
>>  		zpci_ibv[cpu] = airq_iv_create(cache_line_size() * BITS_PER_BYTE,
>> +					       AIRQ_IV_PTR |
>>  					       AIRQ_IV_DATA |
>>  					       AIRQ_IV_CACHELINE |
>>  					       (!cpu ? AIRQ_IV_ALLOC : 0), NULL);
>
>
> This looks very good to me already. Unfortunately, I was unable to
> relieve my MSI vs. MSI-X anxiety regarding arch_restore_msi_irqs() with
> a test since the only MSI-using PCI function (ISM) is not supporting
> PCI auto-recovery :(
>
> But a mlx5 VF now recovers just fine!

Did my expanation above help with this?

Thanks
Tobias